The Global Navigation Satellite Systems (GNSS) generically include the General Positioning System (GPS), operated by the United States, the Global Orbiting Navigation Satellite System (GLONASS) operated by the Russian Federation and the projected Galileo positioning system, to be built by the European Union.
GNSS radio signals are located in the portion of the radio spectrum above 1 GHz, have power level, at ground, of the order of −120 dBm or less and are generally direct-sequence spread-spectrum signals modulated by pseudo-random code binary sequences, which are used in the receiver for positioning and navigation. The signal structure of GPS signals is described, for example, in international patent application WO05003807, in the name of the applicant, which is hereby incorporated by reference.
Satellite radiolocalization systems, such as GPS (Global Positioning System), GLONASS or Galileo rely on the reception of radio signals broadcast from a number of orbiting satellites and use the information contained in these signals to determine the distances, or ranges, from the receiver to each of the received satellites. The orbits of the satellites being known, absolute time and the location of the GPS receiver can then be determined geometrically.
In the context of the present invention the terms “receiver” and “GPS receiver” can designate a complete self-contained receiver device, but also a module, included in a complex entity, for example a GPS module in a cellular phone, a car alarm, a PDA (Portable Digital Assistant) and so forth. The terms above may also indicate a pluggable module, which may be connected with a hosting device by means of an appropriate bus, for example a GPS PC-card.
The terms “receiver” and “GPS receiver” should also be understood, in the context of the present invention, as including one of more integrated circuits, arranged to realize a complete GPS receiver or a complete GPS module, as defined above.
Each of the satellite system in the GNSS has different signal carrier frequency; GPS satellites currently use the L1 and L2 bands, with a foreseen extension in the L5 band, but reception of the L1 signal is sufficient for providing basic functionality. Galileo foresees different carriers in the L1, E1, E2, E5 and E6 bands (see table 1). GLONASS signals are also located in bands L1 and L2. Each of these frequencies requires a specifically designed RF receiving circuit.
Once the Galileo system is fully operational, future receiver may be able to increase the number of visible satellites at any time and the coverage at high latitudes will be improved. To take advantage of this, however, future receiver will have to be able to deal with signals coming from all or at least several frequency bands.
It is an aim of the present invention to provide a multiband GNSS receiver of simple and economical construction.
It is a further aim of the present invention to provide a multiband GNSS receiver which can be easily adapted for receiving signal in a selected set of GNSS bands.